TWiki Plugins

Overview

You can add Plugins to extend TWiki's functionality, without altering the core program code. A plug-in approach lets you:

add virtually unlimited features while keeping the main TWiki code compact and efficient;

heavily customize an installation and still do clean updates to new versions of TWiki;

rapidly develop new TWiki functions in Perl using the Plugin API.

Everything to do with TWiki Plugins - demos, new releases, downloads, development, general discussion - is available at TWiki.org, in the TWiki:Plugins web.

Preinstalled Plugins

TWiki comes with a set of Plugins as part of the standard installation.

DefaultPlugin: Optionally handles some legacy variables from older versions of TWiki. You can control this option from TWikiPreferences. (Perl programmers can also add rules for simple custom processing.)

EmptyPlugin: Is a fully functional module, minus active code; it does nothing and serves as a template for new Plugin development

CommentPlugin: Allows users to quickly post comments to a page without an edit/preview/save cycle.

InterwikiPlugin: Use it for shorthand linking to remote sites, ex: TWiki:Plugins expands to TWiki:Plugins on TWiki.org. You can edit the predefined set of of Wiki-related sites, and add your own

TablePlugin: Control attributes of tables and sorting of table columns

Installing Plugins

Each TWikiPlugin comes with full documentation: step-by-step installation instructions, a detailed description of any special requirements, version details, and a working example for testing.

Most Plugins can be installed in three easy steps, with no programming skills required:

Download the zip file containing the Plugin, documentation, and any other required files, from TWiki:Plugins.

Distribute the files to their proper locations - unzip the zip archive in your TWiki installation directory - if have a standard TWiki installation, this will distribute automatically. Otherwise, place the files according to the directory paths listed on the Plugin top in TWiki:Plugins.

Check the demo example on the Plugin topic: if it's working, the installation was fine!

Special Requests: Some Plugins need certain Perl modules to be preinstalled on the host system. Plugins may also use other resources, like graphics, other modules, applications, templates. In these cases, detailed instructions are in the Plugin documentation.

Each Plugin has a standard release page, located in the TWiki:Plugins web at TWiki.org. In addition to the documentation topic (SomePlugin), there's a separate development page.

Doc page: Read all available info about the Plugin; download the attached distribution files.

Checking that Plugins are Working on a Live Server

A Note on Plugin Performance

The performance of the system depends on the number of Plugins installed and on the Plugin implementation. Some Plugins impose no measurable performance decrease, some do. For example, outsidePREHandler is an expensive callback function, or a Plugin might use many Perl libraries that need to be initialized with each page view (unless you run mod_perl). It is recommended to measure the performance with and without a new Plugin. Example for Unix:time wget -qO /dev/null http://www.denx.de/wiki/view/TWiki/AbcPlugin

In case you need to install an "expensive" Plugin and you need its functionality only in one web you can place the Plugin topic into that web. TWiki will initialize the Plugin only if the Plugin topic is found (which won't be the case for other webs.)

Managing Plugins

When you finish installing a Plugin, you should be able to read the user instructions and go. In fact, some Plugins require additional settings or offer extra options that you have to select. Also, you may want to make a Plugin available only in certain webs, or temporarily disable it. And may want to list all available Plugins in certain topics. You can handle all of these management tasks with simple procedures.

Setting Preferences

Installed Plugins can be toggled on or off, site-wide or by web, through TWikiPreferences and individual WebPreferences:

All Plugin modules present in the lib/TWiki/Plugins directory are activated automatically unless disabled by the DISABLEDPLUGINS Preferences variable in TWikiPreferences. You can optionally list the installed Plugins in the INSTALLEDPLUGINS Preferences variable. This is useful to define the sequence of Plugin execution, or to specify other webs than the DENX web for the Plugin topics. Settings in TWikiPreferences are:

Set INSTALLEDPLUGINS = DefaultPlugin, ...

Set DISABLEDPLUGINS = EmptyPlugin, ...

Plugin execution order in TWiki is determined by searching Plugin topics in a specific sequence: First, full web.topicname name, if specified in INSTALLEDPLUGINS; next, the TWiki web is searched; and finally, the current web.

Plugin-specific settings are done in individual Plugin topics. Two settings are standard for each Plugin:

One line description, used to form the bullets describing the Plugins in the TextFormattingRules topic:

Set SHORTDESCRIPTION = Blah blah woof woof.

Debug Plugin, output can be seen in data/debug.txt. Set to 0=off or 1=on:

Set DEBUG = 0

The settings can be retrieved as Preferences variables like %<pluginname>_<var>%, ex: %DEFAULTPLUGIN_SHORTDESCRIPTION% shows the description of the DefaultPlugin.

Listing Active Plugins

Plugin status variables let you list all active Plugins wherever needed. There are two list formats:

The %PLUGINDESCRIPTIONS% variable displays a bullet list with a one-line description of each active Plugins. This variable is based on the %<plugin>_SHORTDESCRIPTION% Preferences variables of individual topics and is shown in TextFormattingRules.

TablePlugin: Control attributes of tables and sorting of table columns

The TWiki Plugin API

The Application Programming Interface (API) for TWikiPlugins provides the specifications for hooking into the core TWiki code from your external Perl Plugin module. The Plugin API is new to the Production version of TWiki with the 01-Sep-2001 release.

Available Core Functions

The TWikiFuncModule (lib/TWiki/Func.pm) implements ALL official Plugin functions. Plugins should ONLY use functions published in this module.

If you use functions not in Func.pm, you run the risk of creating security holes. Also, your Plugin will likely break and require updating when you upgrade to a new version of TWiki.

Predefined Hooks

In addition to TWiki core functions, Plugins can use predefined hooks, or call backs, listed in the lib/TWiki/Plugins/EmptyPlugin.pm module.

All but the initPlugin are disabled. To enable a call back, remove DISABLE_ from the function name.

For best performance, enable only the functions you really need. NOTE: outsidePREHandler and insidePREHandler are particularly expensive.

Most Plugins use either the commonTagsHandler or startRenderingHandler for rendering tasks:

commonTagsHandler: Use it to expand %XYZPLUGIN% and %XYZPLUGIN{...}% variables

startRenderingHandler: Use it for your own rendering rules or to overload TWiki's internal rendering like [[links]]

Plugin Version Detection

To eliminate the incompatibility problems bound to arise from active open Plugin development, a Plugin versioning system is provided for automatic compatibility checking.

All modules require a $VERSION='0.000' variable, beginning at 1.000.

The initPlugin handler should check all dependencies and return TRUE if the initialization is OK or FALSE if something went wrong.

The Plugin initialization code does not register a Plugin that returns FALSE (or that has no initPlugin handler).

$TWiki::Plugins::VERSION in the TWiki::Plugins module contains the TWiki Plugin API version, currently 1.025.

You can also use the %PLUGINVERSION{}% variable to query the Plugin API version or the version of installed Plugins.

Creating Plugins

With a reasonable knowledge of the Perl scripting language, you can create new Plugins or modify and extend existing ones. Basic plug-in architecture uses an Application Programming Interface (API), a set of software instructions that allow external code to interact with the main program. The TWiki Plugin API Plugins by providing a programming interface for TWiki.

The DefaultPlugin Alternative

DefaultPlugin can handle some outdated TWiki variables, found, for example, in sites recently updated from an old version. Settings are in DefaultPlugin topic. You can also add your own simple custom processing rules here, though in all but very simple cases, writing a new Plugin is preferable.

Anatomy of a Plugin

A basic TWiki Plugin consists of two elements:

a Perl module, ex: MyFirstPlugin.pm

a documentation topic, ex: MyFirstPlugin.txt

The Perl module can be a block of code that connects with TWiki alone, or it can include other elements, like other Perl modules (including other Plugins), graphics, TWiki templates, external applications (ex: a Java applet), or just about anything else it can call.
In particular, files that should be web-accessible (graphics, Java applets ...) are best placed as attachments of the MyFirstPlugin topic. Other needed Perl code is best placed in a lib/TWiki/Plugins/MyFirstPlugin/ directory.

The Plugin API handles the details of connecting your Perl module with main TWiki code. When you're familiar with the Plugin API, you're ready to develop Plugins.

Creating the Perl Module

Copy file lib/TWiki/Plugins/EmptyPlugin.pm to <name>Plugin.pm. The EmptyPlugin.pm module contains mostly empty functions, so it does nothing, but it's ready to be used. Customize it. Refer to the Plugin API specs for more information.

If your Plugin uses its own modules and objects, you must include the name of the Plugin in the package name. For example, write Package MyFirstPlugin::Attrs; instead of just Package Attrs;. Then call it using:

Writing the Documentation Topic

The Plugin documentation topic contains usage instructions and version details. It serves the Plugin files as FileAttachments for downloading. (The doc topic is also included in the distribution package.) To create a documentation topic:

Plugin Info: <Version, credits, history, requirements - entered in a form, displayed as a table. Both are automatically generated when you create or edit a page in the TWiki:Plugins web.>"

Packaging for Distribution

A minimum Plugin release consists of a Perl module with a WikiName that ends in Plugin, ex: MyFirstPlugin.pm, and a documentation page with the same name(MyFirstPlugin.txt).

Distribute the Plugin files in a directory structure that mirrors TWiki. If your Plugin uses additional files, include them ALL:

lib/TWiki/Plugins/MyFirstPlugin.pm

data/TWiki/MyFirstPlugin.txt

pub/TWiki/MyFirstPlugin/uparrow.gif [a required graphic]

Create a zip archive with the Plugin name (MyFirstPlugin.zip) and add the entire directory structure from Step 1. The archive should look like this:

lib/TWiki/Plugins/MyFirstPlugin.pm

data/TWiki/MyFirstPlugin.txt

pub/TWiki/MyFirstPlugin/uparrow.gif

Publishing for Public Use

You can release your tested, packaged Plugin to the TWiki community through the TWiki:Plugins web. All Plugins submitted to TWiki.org are available for download and further development in TWiki:Plugins/PluginPackage. Publish your Plugin in these steps:

Link from the doc page to a new, blank page named after the Plugin, and ending in Dev, ex: MyFirstPluginDev. This is the discussion page for future development. (User support for Plugins is handled in TWiki:Support.)